Given the ubiquitous use of ink-jet printers, there are many types of ink-jet printing systems and many types of ink. Despite this variety, foaming of ink within the printing systems is common and can be caused differently from system to system. For example, in some systems, the foaming can be caused by surfactants, which are intended to adjust surface tension of the ink. In some instances, while the presence of negative pressure favorably prevents drooling from nozzles of a printhead, this negative pressure also can allow the ink to be mixed under suction with air, thereby producing more foam or bubbles.
Among other issues associated with foaming of ink, in some systems, the foam enters the supply line of the negative pressure source. This phenomenon can foul operation of the negative pressure system and/or harm the supply line because of the aggressive characteristics of the ink on certain materials.